Preheat oven to 350°F. Line the insides of a 9×13-inch glass baking pan with parchment paper, leaving enough overhang to lift the dessert out (the bars are easier to cut this way). Set aside.
Add the soft butter and sugar to a large mixing bowl. Using a pastry cutter or fork, stir to combine. Add in flour and blend again, creating a thick dough.
Press firmly into prepared pan, making sure the shortbread dough is in an even layer. Bake for 15-20 minutes or until the edges are very lightly browned and firm to the touch.
While the crust cooks, make the filling. Whisk together eggs until smooth. Add sugar, lemon juice, and lemon zest. Mix until combined. Sift in your flour. This is important! Sifted flour ensures no flour clumps!
Remove crust from the oven. Use the tines of a fork to randomly prick holes across the top of the warm crust. Do not poke all the way through! This helps the lemon curd filling to stay on the crust.
Pour the filling into the warm crust. Bake for 20-25 minutes or until the filling is set and no longer jiggly.
Cool at room temperature for 2 hours, then chill in the fridge for 2 hours before cutting the squares. It's important to allow enough time for the filling to set up.
Once cool, lift the parchment paper to remove the dessert from the pan. Dust the top with powdered sugar, then cut into squares for serving.
Cover and store leftover lemon bars in the refrigerator for up to 1 week.
Notes
Avoid using a metal baking pan. Some people notice a metallic flavor in lemon desserts baked in metal pans, so a glass or ceramic baking pan is best.
Line your pan with parchment paper to make the bars easier to remove.
Use freshly squeezed lemon juice for the best flavor.
Be careful not to over bake the crust the color should be barely golden brown.
Chill for at least 2 hours before attempting to cut into squares.
Do not be concerned if you notice a layer of air bubbles on top of the baked filling. This is completely normal. A dusting of powdered sugar hides them well.